This invention relates to additive compositions, otherwise known as admixtures, for incorporation in hydraulic cement mixes, for example, hydraulic cement concretes, mortars, and grouts, neat cement mixes, concrete blocks mixes, and dry mixes for making such concretes, mortars, and grouts, especially to increase the compressive strength of the hardened mix.
Admixtures are employed to achieve, among other things, water reduction, improved compressive strength, and retardation of the rate of hardening and setting of cement mixes. Frequently, greater compressive strengths are obtained when reduced quantities of water are utilized in hydraulic cement mixes, and so often water reduction and increased compressive strength are achieved together. Admixtures which increase compressive strength may also produce a retardation of the rate of set of the hydraulic cement mix. As retarders, such admixtures slow the chemical process of hydration so that the concrete remains plastic and workable for a longer time than concrete without such a retarder, which can result in increased hydration of the cement and ultimately increased compressive strengths. Although compressive strength improving admixtures can and usually do possess and produce additional features, they are valuable and desirable because of the increased compressive strength. Among the materials commonly used for improved compressive strength are the lignosulfonates, such as calcium lignosulfonate; salts of hydroxycarboxylic acids; sugars such as glucose (dextrose), maltose, sucrose, fructose, and the like; and highly polymerized polysaccharides, such as dextrins. These materials can produce additional results such as water reduction and/or retardation of the rate of set.
Other admixtures, known to increase the compressive strength of the hardened mix, also produce additional effects on the mix such as entraining air in the mix, or change the character of the mix, such as the stickiness or finishability of the mix. So, an admixture which could improve the compressive strength of the hardened mix without producing any other changes would be desirable.
Often, additives or admixtures are frequently used in combinations to achieve certain results or overcome inefficiencies or other features, such as where an admixture does produce a sufficient or significant improvement in the compressive strength, but also effects a significant degree of retardation. To overcome or compensate for these effects, whether desirable or not, such as for example, the excessive amount of retardation, well known accelerators, such as calcium chloride and triethanolamine, that increase the rate of hydration for early strength development are frequently used. In addition, an admixture which increased compressive strength without affecting other features would be useful where the beneficial features of other admixtures could be combined to emphasize the additional other features. Thus, admixtures which can be used in combination with other admixtures are also desirable.
Further, the problem of unavailability would apply to any new and improved admixture. Increasing demands can make admixtures unavailable. Lignosulfonates, for example, are not as ubiquitously available as they once were due to the pressure of, among others, environmental restrictions which have forced suppliers to find means of consuming these materials through their own corporate channels. Also, sugars and dextrins are subject to the whims and fancies of speculative interests, and so have become quite costly, as well as occasionally being unavailable.
Thus a need exists for additive compositions, or admixtures, for incorporation in hydraulic cement mixes, which additives will provide improved compressive strength for the resulting cement products.